1. Field of the Invention
The present invention relates to improvement of a visual axis detection apparatus used in a camera using a film, a video camera, and so on.
2. Related Background Art
A conventional method of calculating a position of a Purkinje image (a corneal reflection image) is disclosed, for example, in Japanese Patent Application Laid-Open No. 61-172552 or the like. FIG. 13 shows this conventional embodiment disclosed in Japanese Patent Application Laid-Open No. 61-172552.
If a light emitting element (not shown) is lighted with alternating current by a driver circuit, a four-divisional element or a semiconductor position detector (PSD) 31, and a circuit 40 measure the position of an image of the Purkinje effect, which is digitized by an A/D converter (not shown) to be input into a control circuit.
In the above-mentioned conventional apparatus, however, the following problem arises.
That is, in the conventional apparatus, the center of gravity of the Purkinje image is obtained by calculating the center of gravity of the light image formed on the two-dimensional semiconductor element (two-dimensional PSD) by means of the digital circuit. Accordingly, if a signal similar to the Purkinje image such as tears of an observer, a ghost image or the like of the spectacles worn by the observer, or the like exists, or if an extremely high luminous light image is formed by light coming from outside or the like, bad effects thereof make it difficult to precisely obtain the position of the Purkinje image.